The present invention relates to a catalyst containing platinum on a carbon carrier for the catalytic oxidation of glyoxal to provides glyoxylic acid with good activity, selectivity and yield. In another aspect, the present invention relates to the method of producing the catalyst and the method of making glyoxylic acid.
Glyoxylic acid is obtained on an industrial scale by means of the oxidation of glyoxal with strong acids such as nitric acid. Electrochemical methods are also described in the literature.
EP 0,438,948 A1 describes the direct catalytic oxidation of glyoxal by means of heterogeneous carrier catalysts to glyoxylic acid. In example 1 of this patent a optimized catalyst is prepared in that at first the activated carbon carrier is partially burned after an HCl wash at 500.degree. C. in a current of air, which results in an elevation of its specific carrier surface. This is followed by impregnating the carrier treated in this manner with an aqueous solution of hexachloroplatinic acid, treating with formaldehyde, converting with potassium hydroxide and subsequently washing and drying. The catalyst obtained in this manner exhibits a homogeneous distribution of platinum particles in a range of 1.5 to 2 nm.
The catalyst produced according to EP 0,438,948 and containing 4.2% platinum when used in the catalytic oxidation of glyoxal results in a yield of 73% and a selectivity of 79.3% of glyoxylic acid. The ratio of catalyst to glyoxal used in the reference is indicated at about 43% by weight. A catalytic activity of 1.24 mmoles glyoxylic acid per mmole platinum per minute can be calculated for the reaction time of 110 minutes indicated in example 1 of EP 0,438,948.
The partial combustion of the activated carbon carrier and the further steps of the preparation of the catalyst are apparently essential for the effective utilization of the platinum-containing, catalytically active phases of EP 0,348,948.
Unfortunately, decisive steps for the production of the catalyst can not be reproduced from the art. Although the partial combustion of the activated carbon is an essential step of this catalytic preparation, any indication of the amount required as well as of the resulting quantity of activated carbon obtained after partial burning is lacking for this. In addition, it has been found that many steps of this catalytic preparation are very complicated. For example, the conversion of the activated carbon with nitric acid is carried out for 24 hours.
One of the objects of the present invention is to provide a catalyst for the oxidation of glyoxal to produce glyoxylic acid which is distinguished from the catalysts of the state of the art by a lower noble metal requirement and an improved economy resulting therefrom. A further object of the present invention concerns a method of producing this catalyst.